Conventionally, inorganic photoconductive substances such as selenium, zinc oxide, cadmium sulfide and silicon have widely been used in an electrophotographic photosensitive body. Those inorganic substances had many advantages and simultaneously had various disadvantages. For example, selenium has the disadvantages that its production conditions are difficult and it is liable to crystallize by heat or mechanical shock. Zinc oxide and cadmium sulfide have problems in moisture resistance and mechanical strength, and have the disadvantage such that electrostatic charge and exposure deterioration take place by a coloring matter added as a sensitizer, thus lacking in durability Silicon involves that its production conditions are difficult, cost is expensive because of using a gas having strong irritating properties and care should be taken to handling because of being sensitive to humidity. Additionally selenium and cadmium sulfide have the problem in toxicity.
Organic photosensitive bodies using various organic compounds that improved disadvantages of those inorganic photosensitive bodies are widely used. Organic photosensitive bodies include a single layer photosensitive body having a charge generating agent and a charge transport agent dispersed in a binder resin, and a multi-layered photosensitive body having a charge generating layer and a charge transport layer functionally separated. The characteristics of such a photosensitive body called a functional separation type are that a material suitable to the respective function can be selected from a wide range, and a photosensitive body having an optional function can easily be produced. From such a situation many investigations have been carried out.
As described above, to satisfy requirements such as basic performances required in electrophotographic photosensitive bodies and high durability, various improvements have been made in development of new materials, their combinations and the like, but it is the present situation that satisfactory photosensitive bodies are not yet obtained.
As one example of the above, it is generally known that when various photosensitive bodies are prepared by varying a binder resin to a specific charge transport agent, the kind of the binder resin affects film properties and electrophotographic characteristics of the photosensitive body. For example, when a photosensitive body is prepared using a polystyrene resin as a binder resin to a stilbene charge transport agent, electrophotographic characteristics represented by drift mobility and sensitivity are improved, but reversely the film becomes brittle and film properties deteriorate. Further, when a photosensitive body is prepared using an acrylic acid ester resin as a binder resin, electrophotographic characteristics deteriorate though film properties become good.